1. Field of the Invention
The instant invention relates generally to tunnel ventilation systems and, more particularly, to tunnel ventilation systems having fire responsive dampers or other fusible closures.
2. Description of the Prior Art
Numerous structures exist which combine some form of fusible link with a window or other form of damper. When the fusible link is exposed to the heat of a fire it fuses and the window or damper opens. Such devices are typically employed in buildings such as homes. (See e.g. U.S. Pat. Nos. 609,278 and 1,380,207).
Still another technique of providing fire ventilation using fusible materials is that disclosed in U.S. Pat. No. 2,416,284. This latter patent discloses the use of panels of fusible material which form at least a part of the roof of a building. In the event of a fire, the roof panels fuse, creating openings in the roof, thereby providing ventilation into the atmosphere.
Many tunnels employ forced and ducted ventilation systems. Such systems rely on the fixed sized openings used for "normal" ventilation to also provide smoke control and removal in the event of a fire. The actual size of the ventilation openings compared to the vehicular space, the quantity of smoke generated, and the proximity of these openings to a roadway fire are major factors in the efficacy of the smoke control and removal, and systems in which the normal ventilation openings are used for this purpose are severely limited in their smoke removal capability.
Other tunnels employ systems which depend on motorized dampers. These latter systems require periodic maintenance to be operable when needed and have other disadvantages.